Transportation equipment emits CO2 and other greenhouse gases. Therefore, efforts are being made to provide increased fuel efficiency based on various means in order to prevent global warming. Particularly, automobiles account for the great majority of the transportation equipment. Therefore, it is highly demanded that the automobiles provide increased fuel efficiency. As such being the case, researches and commercialization are being made to provide increased fuel efficiency by reducing the weight of automobile bodies and making full use of hybrid technologies.
A comfortable ride in an automobile depends, for example, on unsprung weight. More specifically, if the unsprung weight, that is, the total weight of unsprung components such as suspensions, tires, and wheel rims, is small, the suspensions react properly to provide a comfortable ride. If, by contrast, the unsprung weight is great, the suspensions react improperly to provide degraded ride quality.
In order to maintain a comfortable ride in an automobile and provide increased fuel efficiency based on automobile body weight reduction, it is necessary to not only reduce the weight of the whole automobile body by reducing the weight of a body and other parts positioned above the suspensions, but also reduce the weight of an automobile undercarriage component positioned below springs.
Some technologies have been proposed in order to reduce the weight of an automobile undercarriage component. An automobile undercarriage component formed of an aluminum alloy having a through-hole is disclosed, for instance, in Patent Literature 1. A normal portion of the automobile undercarriage component, which is without coarsened crystal grains, has a yield stress of 270 MPa or higher, and the minimum length between the end of a rib portion, which is a predetermined portion of a rib that is positioned toward the through-hole, and the end of a through-hole portion, which is a predetermined portion of a web that is positioned toward the through-hole, is 6 mm or more.